Editing Celestial sphere

[[Category: Astronomy]]
== Explanation ==
A celestial sphere is an arbitrary sphere assumed by humans on [[Earth]] when they started observing the stars. It is assumed that the center of the celestial sphere is the Earth, such that the [[pole]]s and [[equator]] of both the Earth and the celestial sphere aligns with each other. The celestial sphere or more generally, the celestial sky is used as a reference point for navigation in the earlier times. Just like our local star, [[Sun]], the stars in the celestial sky, appear to set in the west and rise in the east due to Earth's rotation. Any star can be located on the celestial sky with two coordinates [[declination]] and [[right ascension]], which are analogous to the Earth's [[latitude]] and [[longitude]].

== Frequently Asked Questions ==
=== Are all stars fixed in the celestial sphere? ===
The position of the [[star]]s, [[nebula]]e and [[galaxy|galaxies]] are assumed to be fixed in the celestial sky. Their positions do change, but the relative distances between them seldom change. As the distance between the Earth and the stars are seemingly long, they make a negligible movement due to minuscule angles that are almost zero. Using [[small-angle approximation]], the positions of stars are simplified and assumed to be fixed.

=== Is the position of the Sun fixed? ===
As Earth rotates around the Sun, in fixed Earth and celestial sphere sense, it would appear that the Sun follows its own path around the Earth throughout one Earth year relative to the stars in the celestial sphere. This path is known as the [[ecliptic]], which marks the [[Tropic of Cancer]] and [[Tropic of Capricorn]] on Earth.